The present invention relates to a toroidal transmission, especially for motor vehicles, comprising an input shaft which can be connected to an engine, a first toroidal variator and a second toroidal variator which are connected to the input shaft on the input side, a first output shaft which can be connected to the output of the first toroidal variator, and a second output shaft which can be connected to the output of the second toroidal variator.
Such a toroidal transmission is disclosed, for example, by EP 0 743 218 B1.
Toroidal transmissions have long been known in the art. They permit a continuously variable adjustment of the transmission ratio. Toroidal transmissions have hitherto been designed for standard vehicles having one powered axle.
A known concept for a toroidal transmission T (cf. FIG. 4) for motor vehicles comprises two toroidal variators V1, V2, which have a common hollow input shaft VE. The hollow input shaft VE is fixed to a countershaft VW, which is in turn connected by way of a fixed gear train to an output shaft E of an internal combustion engine.
The outputs VA1, VA2 of the toroidal variators V1, V2 are connected to one another and via an output shaft are connected to a sun gear of a planetary gear train P (summing gear set). A planet carrier of the planetary gear train is connected by way of a further fixed gear train to the countershaft. The internal gear (ring gear) of the planetary gear train is connected by way of a “low-range clutch” L to the output shaft of the toroidal transmission. The sun gear—and consequently the output shaft of the toroidal variators—is likewise connected by a “high-range clutch” H to the output shaft.
In this conventional gear train the toroidal transmission can be operated in two ranges, the “low” regime and the “high” regime. In the low regime the low-range clutch L is closed. In this case power is circulated in the transmission. The so-called “geared neutral” can thereby be achieved. In the high regime the high-range clutch H is closed. The drive power flows from the output shaft of the toroidal variators V1, V2 directly to the output A.
In the known toroidal transmission the two toroidal variators V1, V2 are arranged parallel to one another. In the low regime they are connected to the output shaft by way of the planetary gear train (summing gear set), in the high regime they are connected directly to the output shaft.
In standard vehicles the output shaft A of the toroidal transmission T is connected to the one powered axle.
Connecting the output shaft of the toroidal transmission to the input of a transfer case is also known in four-wheel drive vehicles. The transfer case transmits a certain percentage of the input power to a first powered axle (for example the front axle) and the remainder of the input power to a second powered axle (for example the rear axle).
Transfer cases, however, mean additional weight and take up additional overall space. Where the transfer case does not function purely mechanically, an additional control is needed for the transfer case.
The aforementioned EP 0 743 218 B1 discloses a toroidal transmission having two toroidal variators. The output of the one toroidal variator is connected to a differential, which transmits 50% of the input power to a front axle and 50% to a rear axle. The output of the other toroidal variator is connected directly to the rear axle and consequently transmits 100% of the torque to the rear axle. Accordingly in this toroidal transmission a torque distribution of 25%:75% is set up between the front axle and the rear axle in normal operation. However, no facility for power range shifting is provided. Nor can a “geared neutral” be achieved using the transmission.
In this known toroidal transmission the output of the one toroidal variator is assigned exclusively to the front axle, and the output of the other toroidal variator exclusively to the rear axle. The gear train structure described above with a low-range clutch and a high-range clutch is doubled in this mode, so that a power range shifting is feasible.